Generally, a geomagnetic sensor is a device that detects very minute geomagnetism to identify a point of the compass. Therefore, a geomagnetic sensor is likely to be influenced by magnetism from peripheral magnetic sources. Thus, a geomagnetic sensor is likely to cause some deviation in detection depending upon the environment. In order to obtain an accurate measurement result, a correction process of a geomagnetic sensor, called calibration, should be performed in a proper manner.
In a case where a geomagnetic sensor is installed at a fixed position, even if a correction process is not so frequently performed, a measurement result can be obtained from a geomagnetic sensor with sufficient accuracy as long as the geomagnetic sensor keeps the same positional relationship with peripheral magnetic sources. However, since a mobile device such as a cellular phone has characteristics of a carried device, the environment where a geomagnetic sensor is used changes frequently. A mobile device including a geomagnetic sensor is described in JP-A 2005-207799 (hereinafter referred to as Patent Literature 1). In a case where a geomagnetic sensor is included in a mobile device, a measurement result cannot be obtained with sufficient accuracy unless a correction process is performed more frequently than a fixed type geomagnetic sensor because the presence of peripheral magnetic sources, the positional relationship, and the like are not kept constant.
Meanwhile, a certain period of time is required for a correction process of a geomagnetic sensor. In order to perform a correction process, a user conducts an operation of orienting a geomagnetic sensor of a mobile device preferably toward the north and rotating it around a specific axis a plurality of times. If a user is often required to conduct such an operation, the operability of the mobile device is impaired, thereby causing stress to the user.
In a conventional cellular phone including a geomagnetic sensor, a general procedure is as follows: A message to urge an execution of a correction process of the geomagnetic sensor is displayed on an LCD (Liquid Crystal Display) each time the geomagnetic sensor is activated or at regular intervals. A user sees the message and conducts a correction process.
In the case where a correction process is performed each time a geomagnetic sensor is activated, a user is required to conduct the aforementioned operation including rotation of the mobile device each time he/she uses the geomagnetic sensor. The user conducts the operation in response to the request, awaits completion of the correction process, and then obtains a measurement result of the geomagnetic sensor. However, such a procedure is likely to impair the operability and cause stress to the user.
In the case where a correction process is performed at regular intervals, sufficient accuracy can be obtained if the intervals are sufficiently shortened. However, a user is required to conduct frequent operations. If the intervals are lengthened, the measurement accuracy of the geomagnetic sensor is lowered while the frequency of the operation requests to the user is lowered. How to determine an appropriate length of the intervals becomes an issue. However, an appropriate length of the intervals depends upon the frequency at which the user moves and the like. Thus, it is difficult to determine an appropriate length of the intervals.
Furthermore, in either case, whether or not to perform a correction process depends upon the user. Some users may conduct no correction process or may rarely conduct a correction process. Constant reliability of the measurement results cannot be expected.